As a method for producing a fluorine-containing carboxylic acid ester, there are known (1) a method of esterifying a fluorine-containing carboxylic acid in the presence of an acid catalyst, (2) a method of reacting 1-alkoxy-1,1,2,2-tetrafluoroethane, sulfuric acid, and silica (Non-patent Publication 1), (3) a method of reacting difluoroacetic acid fluoride, which is obtained by subjecting 1-alkoxy-1,1,2,2-tetrafluoroethane to a gas-phase reaction in the presence of a metal oxide catalyst, with an alcohol (Patent Publication 1), etc.
In the method of (1), there is a problem that difluoroacetic acid as the raw material is not easily available. As a method for producing difluoroacetic acid, there have been reported (4) a method in which chlorotrifluoroethylene as a starting material is reacted with an alkylamine, followed by hydrolysis to obtain a chlorofluoroacetic amide, moreover fluorination to convert it into difluoroacetic amide, and then hydrolysis (Non-patent Publication 2), (5) a method in which ammonia is added to tetrafluoroethylene to prepare 2,4,6-difluoromethyl-1,3,5-triazine, followed by hydrolysis (Patent Publication 2), etc.
In the method of (4), however, there are problems that the fluorination of chlorofluoroacetic amide is a reaction of a long time and a high temperature, that a post-treatment after the fluorination is complicated, and that yield is also low. Furthermore, in the method of (5), an industrial execution is difficult, since the addition of tetrafluoroethylene and ammonia is a high-pressure reaction of a gauge pressure of 3.4 MPa (34 kgG/cm2).
Furthermore, in each method of (4) and (5), a hydrolysis step is necessary. When using a hydrolysis step using sulfuric acid, there is a problem that a large amount of sulfuric acid waste liquid occurs. Furthermore, in the case of using a hydrolysis step using an alkali metal hydroxide aqueous solution, difluoroacetic acid is obtained as a mixture of water and an inorganic salt. Since difluoroacetic acid has a boiling point higher than that of water, there is a problem that separation from the inorganic salt by distillation is difficult, and recovery is low.
Furthermore, in the method of (2), it is difficult to control the reaction, and there is a risk that the reactor may corrode. Furthermore, the method of (3) is composed of a two-step reaction in which difluoroacetic acid fluoride is once produced from 1-alkoxy-1,1,2,2-tetrafluoroethane, and an alcohol is reacted with it. In more detail, it is composed of complicated steps that the alkoxy group moiety is eliminated as an alcohol by the first step reaction, and the alcohol is again added in the second step. In such reaction process, it is necessary to have a large-scale reaction apparatus and complicated operations. Furthermore, there is a risk that resources may be wasted by dumping a part of the raw material, and an excessive energy may be consumed.    Non-patent Publication 1: J. Am. Chem. Soc., 72, 1860 (1950)    Non-patent Publication 2: Collect. Czech. Chem. Comm., 42(8), 2537 (1977), CS180697    Patent Publication 1: Japanese Patent Application Publication 8-92162    Patent Publication 2: U.S. Pat. No. 2,442,995 specification